This invention relates generally to deburring or radiusing, and more specifically to deburring or radiusing articles made of TZM.
Molybdenum is often used as a base material for high-temperature alloys. A growing demand for a further improvement in high temperature properties of molybdenum was the basis for the increasingly widespread use of TZM. TZM is a molybdenum-based alloy that contains small additions of finely dispersed particles, for example, about 0.5% titanium, about 0.08% zirconium, and between about 0.01% to about 0.04% carbon. The addition of these particles serves to inhibit the grain growth of molybdenum at high temperatures, thus increasing the high-temperature strength of molybdenum. TZM is widely used as, for example, a vacuum furnace hot-zone material, a hot die and mold material, x-ray tube target and cathode cup material, or material for parts in numerous aerospace products.
Electrochemical machining of articles or workpieces typically takes place in an electrolyte solution having a high ionic strength. In this method, the workpiece to be machined serves as the anode and the tool electrode of the electrochemical machining apparatus serves as the cathode. During electrochemical machining, an electric current, by means of a power supply, runs between the anode and the cathode. The electrolyte, usually a simple salt solution, is delivered to the gap in between the anode and the cathode. This combination creates an electrolytic cell in which an electrochemical process will cause controlled erosion of the workpiece. The tool electrode acts as a shaping tool and the workpiece, which workpiece serves as the anode, dissolves locally. The conventional electrochemical machining process, as shown in FIG. 1, employs a continuous current across the gap.
Electrochemical deburring and radiusing are widely applied, cost-effective processes for different alloys. Each alloy, however, requires different process conditions in order to achieve desired results. Therefore, it is necessary to understand the process parameters that will allow for desired results in radiusing or deburring TZM.
Radiusing is the process by which the sharp corners of different alloys are removed and the corner is rounded. Deburring is the process of removing little spikes, or burrs, from the corner edges of an alloy in order to have a smooth surface on the corner.
The conventional electrochemical deburring and radiusing methods, as shown in FIG. 1, use a simple salt electrolyte, such as an aqueous sodium chloride or sodium nitrate solution, and a continuous DC current applied across a gap 14 between a tool electrode 10 and a TZM workpiece 12. This method on TZM, however, produces unsatisfactory surface defects in TZM such as pitting and stray current attacking. Pitting is corrosion on the surface of the TZM workpiece, while stray current attacking is the removal and corrosion of the workpiece on an unfocused area. A continuous DC current creates these problems because the current will dissolve the metal beyond the localized area to be machined. A continuous DC current is not suitable for a precision process such as radiusing or deburring of TZM. Also, a method where a sodium chloride electrolyte solution is used results in poor radiusing results for TZM, while a method employing a sodium nitrate solution results in poor surface quality of the TZM workpiece. Therefore, process modifications are needed to improve the surface quality.
Accordingly, there is a need in the art for an improved method for electrochemically deburring or radiusing TZM articles.